Quick and dirty move to GLEW

-Removed manual OpenGL enumeration
-Removed r_log (frame logging wrappers)
-Removed support for installable client drivers
-Removed some 3Dfx specific code paths
-Switched to using GLEW for OpenGL enumeration
-Renamed qgl* functions to gl*
Initial support for glFenceSync

-Adds r_fencesync cvar
-Forces command synchronization immediately after buffer swap
-Defaults to off
-Removed some extraneous rebinding/clear commands